1. Technical Field
The present invention relates to a liquid crystal display and an electronic apparatus.
2. Related Art
Liquid crystal displays (transflective liquid crystal displays) that utilize external light in bright places in a manner similar to that of normal reflective liquid crystal displays and make the display visible with an internal light source in dark places have been proposed. Such a liquid crystal display uses a display system that is both reflective and transparent to achieve a clear display even in darkness as well as to lower power consumption by switching the display mode between the reflection mode and the transparent mode according to the surrounding brightness.
It is considered preferable that a transflective liquid crystal display has a multigap structure such as shown in JP-A-2004-219553 to effectively carry out reflective display and transparent display.
A semi-transmissive reflective liquid crystal display having a multigap structure will be now described.
A liquid crystal display 100 contains a liquid crystal cell 110 and a backlight 120 (a lighting system), as shown in FIG. 8. In the liquid crystal cell 110, a lower substrate 130 and an upper substrate 140 are placed facing each other, with a liquid crystal layer 160 formed therebetween. The backlight 120 is placed on the rear surface side of the liquid crystal cell 110 (on the external surface side of the lower substrate 130).
A semi-transmissive reflecting layer 180 having a metal film with a high reflectance is formed on the inner surface side of the lower substrate 130 that is composed of a translucent material, such as glass and plastic. An orifice 180a is placed for each pixel, on the semi-transmissive reflecting layer 180, for transmitting the light emitted from the backlight 120. Within the forming area of the semi-transmissive reflecting layer 180, the part on which a metal film is actually formed constitutes a reflective display area R while the orifice 180a on which a metal film is not formed constitutes a transflective display area T.
Further, a color filter layer 150 (150R and 150T) composed of a color filter for reflective display 150R and a color filter for transparent display 150T is placed on the inner surface side of the lower substrate 130. The color filter for reflective display 150R is placed on the semi-transmissive reflecting layer 180, which corresponds to the reflective display area R, while the color filter for transparent display 150T is placed on the orifice 180a of the semi-transmissive reflecting layer 180, which corresponds to the transparent display area T.
On the position that corresponds to the reflective display area R of the color filter layer 150, a terraced part 210, such as a resin layer, and a phase contrast layer 200 are sequentially laminated.
The phase contrast layer 200 gives a phase shift of about 100 to 200 nm to the incident visible light transmitted to the liquid crystal cell 110, working as a quarter wavelength plate to the visible light. The phase contrast layer 200 is composed as a polymer liquid crystal that is formed by photo polymerization, for example, of a liquid crystal monomer.
The terraced part 210 is composed of an insulating material, such as an acrylic resin, and is protruded to the liquid crystal layer 160. The terraced part 210, the thickness of which is almost half of the liquid crystal layer thickness, works as an adjusting layer of the liquid crystal layer thickness for making the liquid crystal layer thickness smaller on the reflective display area R than on the transparent display area T. Specifically, the optical path length for transparent display and the optical path length for reflective display can be made almost equal by placing the terraced part 210 on the reflective display area R.
Further, a pixel electrode 230 composed of a transparent conductive material, such as ITO, is formed on the lower substrate 130 in a manner of covering the phase contrast layer 200, the terraced part 210 and the color filter layer 150. Moreover, an alignment layer 240 composed of polyimide or the like is laminatedly formed in a manner of covering the pixel electrode 230. A lower polarizing plate 280 is placed on the external surface side of the lower substrate 130.
Meanwhile, a common electrode 320 composed of a transparent conductive material, such as ITO, and an alignment layer 330 composed of polyimide or the like are sequentially laminated on the internal surface side of the upper substrate 140 that is composed of a translucent material, such as glass or plastic. An upper polarizing plate 360 is placed on the external surface side of the upper substrate 140.
In this way, a multigap structure, such as described above, has a transparent display area T and a reflective display area R within one pixel, with a terraced part 210 formed on their boundaries with a resin layer or the like.
However, having a resin layer (a terraced part), such as described above, has resulted in problems, such as mentioned below. Specifically, placing a resin layer, such as described above, usually causes an inclined plane to be formed on the terraced part. Light will not be reflected efficiently on such an inclined plane. Further, it is not preferable in terms of optimizing the intensity of an output light (a reflected light and a transmitted light) because the optical path length changes continuously on the part corresponding to the inclined plane. There is also a problem that contrast is easily lowered due to decrease in the intensity of output light or to reflection (or transmission) of unnecessary light. There is an option of placing a resin layer in a manner so that an inclined plane may not be formed. In such a case, however, the angle of the angled part, shown as E in the drawing, becomes so small (less than 90 degrees) that the adhesiveness of the phase contrast layer 200, the pixel electrode 230, the alignment layer 240 and the like may be drastically degraded, which causes degradation of the reliability and the durability of the entire liquid crystal display.
Further, a resin layer, such as described above, produces dead space, which is disadvantageous in terms of making devices thinner. There also has been a problem that the liquid crystal alignment is disrupted at the terraced part on the boundaries, which causes degradation of the optical properties.
There also has been another problem that the viewing angle is narrow in a semi-transmissive reflective liquid crystal display.